Perception Of Speech Sounds Research Articles

Enhanced Sensitivity to Subphonemic Segments in Dyslexia: A New Instance of Allophonic Perception.

Although dyslexia can be individuated in many different ways, it has only three discernable sources: a visual deficit that affects the perception of letters, a phonological deficit that affects the perception of speech sounds, and an audio-visual deficit that disturbs the association of letters with speech sounds. However, the very nature of each of these core deficits remains debatable. The phonological deficit in dyslexia, which is generally attributed to a deficit of phonological awareness, might result from a specific mode of speech perception characterized by the use of allophonic (i.e., subphonemic) units. Here we will summarize the available evidence and present new data in support of the “allophonic theory” of dyslexia. Previous studies have shown that the dyslexia deficit in the categorical perception of phonemic features (e.g., the voicing contrast between /t/ and /d/) is due to the enhanced sensitivity to allophonic features (e.g., the difference between two variants of /d/). Another consequence of allophonic perception is that it should also give rise to an enhanced sensitivity to allophonic segments, such as those that take place within a consonant cluster. This latter prediction is validated by the data presented in this paper.

Musical instrument categorization is highly sensitive to spectral properties of earlier sounds

Auditory perception is shaped by spectral properties of surrounding sounds. For example, when spectral properties differ between earlier (context) and later (target) sounds, this can produce spectral contrast effects (SCEs; i.e., categorization boundary shifts) that bias perception of later sounds. SCEs influence perception of speech and nonspeech sounds alike. When categorizing vowels or consonants, SCE magnitudes increased linearly with greater spectral differences between contexts and target speech sounds [Stilp et al. (2015) JASA; Stilp & Alexander (2016) POMA; Stilp & Assgari (2017) JASA]. Here, we tested whether this linear relationship between context spectra and SCEs generalizes to nonspeech categorization. Listeners categorized musical instrument targets that varied from French horn to tenor saxophone. Before each target, listeners heard a one-second music sample processed by spectral envelope difference filters that amplified / attenuated frequencies to reflect the difference between horn and saxophone spectra. By varying filter gain, filters reflected part of (25%, 50%, 75%) or the full (100%) difference between instrument spectra. As filter gains increased to reflect more of the difference between instrument spectra, SCE magnitudes increased linearly, parallel to speech categorization. Thus, a close relationship between context spectra and biases in target categorization appears to be fundamental to auditory perception.

The role of segment probability in perception of speech sounds

This study investigates how listeners utilize segment probability in speech perception. In Warner et al. (2014), participants identified gated fragments of all combinations of two segments in English (e.g., diphones /hə/, /dt/, /ab/, /iɛ/). That data was further analyzed to study the influence of segment probability. Overall probability of the second segment (e.g., the probability of /t/ in English), and conditional probability of the second segment given the first segment (e.g., the probability of /b/ given preceding /a/) were calculated from the CMU pronunciation dictionary. There were significant correlations between accuracy of segment perception and both overall and conditional probability of second segments at early gates of the diphone, when few or no acoustic cues to the second segment were available (for example, perception of /b/ in /ab/ by one-third of the way through the /a/). However, when participants had enough acoustic information, the correlation was smaller or non-significant. The present study shows that English listeners utilize probability in identifying English segments when few acoustic cues are available, whereas Dutch listeners in a matched previous study on perception of Dutch (Warner et al. 2005) utilized probability only for a few unusual cases.

Effects of nonlinear frequency compression on the acoustic properties and recognition of speech sounds in Mandarin Chinese.

The present study examined the change in spectral properties of Mandarin vowels and fricatives caused by nonlinear frequency compression (NLFC) used in hearing instruments and how these changes affect the perception of speech sounds in normal-hearing listeners. Speech materials, including a list of Mandarin monosyllables in the form of /dV/ (12 vowels) and /Ca/ (five fricatives), were recorded from 20 normal-hearing, native Mandarin-speaking adults (ten males and ten females). NLFC was based on Phonak SoundRecover algorithms. The speech materials were processed with six different NLFC parameter settings. Detailed acoustic analysis revealed that the high front vowel /i/ and certain compound vowels containing /i/ demonstrated positional deviation in certain processed conditions in comparison to the unprocessed condition. All five fricatives showed acoustic changes in spectral features in all processed conditions. Fourteen Mandarin-speaking, normal-hearing adult listeners performed phoneme recognition with the six NLFC processing conditions. When the cut-off frequency was set relatively low, recognition of /s/ was detrimentally affected, whereas none of the NLFC processing configurations affected the other phonemes. The discrepancy between the considerable acoustic changes and the negligible adverse effects on perceptual outcomes is partially accounted for by the phonology system and phonotactic constraints in Mandarin.

Varying acoustic-phonemic ambiguity reveals that talker normalization is obligatory in speech processing.

The nondeterministic relationship between speech acoustics and abstract phonemic representations imposes a challenge for listeners to maintain perceptual constancy despite the highly variable acoustic realization of speech. Talker normalization facilitates speech processing by reducing the degrees of freedom for mapping between encountered speech and phonemic representations. While this process has been proposed to facilitate the perception of ambiguous speech sounds, it is currently unknown whether talker normalization is affected by the degree of potential ambiguity in acoustic-phonemic mapping. We explored the effects of talker normalization on speech processing in a series of speeded classification paradigms, parametrically manipulating the potential for inconsistent acoustic-phonemic relationships across talkers for both consonants and vowels. Listeners identified words with varying potential acoustic-phonemic ambiguity across talkers (e.g., beet/boat vs. boot/boat) spoken by single or mixed talkers. Auditory categorization of words was always slower when listening to mixed talkers compared to a single talker, even when there was no potential acoustic ambiguity between target sounds. Moreover, the processing cost imposed by mixed talkers was greatest when words had the most potential acoustic-phonemic overlap across talkers. Models of acoustic dissimilarity between target speech sounds did not account for the pattern of results. These results suggest (a) that talker normalization incurs the greatest processing cost when disambiguating highly confusable sounds and (b) that talker normalization appears to be an obligatory component of speech perception, taking place even when the acoustic-phonemic relationships across sounds are unambiguous.

Background Suppression and its Relation to Foreground Processing of Speech Versus Non-speech Streams

Since sound perception takes place against a background with a certain amount of noise, both speech and non-speech processing involve extraction of target signals and suppression of background noise. Previous works on early processing of speech phonemes largely neglected how background noise is encoded and suppressed. This study aimed to fill in this gap. We adopted an oddball paradigm where speech (vowels) or non-speech stimuli (complex tones) were presented with or without a background of amplitude-modulated noise and analyzed cortical responses related to foreground stimulus processing, including mismatch negativity (MMN), N2b, and P300, as well as neural representations of the background noise, that is, auditory steady-state response (ASSR). We found that speech deviants elicited later and weaker MMN, later N2b, and later P300 than non-speech ones, but N2b and P300 had similar strength, suggesting more complex processing of certain acoustic features in speech. Only for vowels, background noise enhanced N2b strength relative to silence, suggesting an attention-related speech-specific process to improve perception of foreground targets. In addition, noise suppression in speech contexts, quantified by ASSR amplitude reduction after stimulus onset, was lateralized towards the left hemisphere. The left-lateralized suppression following N2b was associated with the N2b enhancement in noise for speech, indicating that foreground processing may interact with background suppression, particularly during speech processing. Together, our findings indicate that the differences between perception of speech and non-speech sounds involve not only the processing of target information in the foreground but also the suppression of irrelevant aspects in the background.

Non-native phonetic learning is destabilized by exposure to phonological variability before and after training.

Phonological variability is a key factor in many phonetic training studies, but it is unclear whether variability is universally helpful for learners. The current study explored variability and sleep consolidation in non-native phonetic learning. Two groups of participants were trained on a non-native contrast in one vowel context (/u/) and differed in whether they were also tested on an untrained context (/i/). Participants exposed to two vowels during the test were less accurate in perception of trained speech sounds and showed no overnight improvement. These findings suggest that introducing variability even in test phases may destabilize learning and prevent consolidation-based performance improvements.

Effects of nonlinear frequency compression on Mandarin speech recognition and sound quality perception in hearing-aid users

The aim of the present study is to evaluate the effects of nonlinear frequency compression (NLFC) on Mandarin speech recognition and sound quality perception. Thirty Chinese-speaking, hearing-impaired adults without hearing-aid experiences participated in the study. They were fitted bilaterally with the Phonak behind-the-ear hearing aids. Each participant was evaluated with the Phoneme Perception Test, Mandarin speech recognition, and sound quality perception at post-fitting 0, 4, and 12 weeks with NLFC-on vs. NLFC-off. The NLFC were active at home. Results show significant differences in detection of phonemes of high-frequency components (such as /sa/) between NLFC on and off. The difference between NLFC on and off was significant for consonant and sentence recognition. Duration of NLFC use had significant effects on the recognition of consonants, vowels, and sentences. Regarding the sound quality perception test, there were significant effects of NLFC conditions (on vs. off), duration of NLFC use, and sound types on the four categories of percepts (i.e., loudness, clarity, naturalness, and overall preference). Therefore, NLFC improves the audibility of high-frequency speech signals and provides better recognition of consonants and sentences and perception of sound quality. The benefit of NLFC on speech recognition and sound quality perception requires certain amount of acclimatization.

Efeitos do contato entre categorias fonéticas distintas em contextos de imigração: uma revisão sobre o atrito de língua materna

Ainda são poucos os estudos, sobretudo no Brasil, que buscam investigar o processo de perda da língua materna não patológica e não relacionada ao envelhecimento saudável, aqui tida como atrito linguístico, fenômeno frequente na produção e percepção dos sons da fala por imigrantes. Este trabalho de cunho qualitativo e bibliográfico, então, tem como objetivo apresentar um panorama sobre o atrito linguístico e sobre os efeitos do contato entre categorias fonéticas distintas na produção do Voice Onset Time por imigrantes em contexto de L2 dominante, buscando também discutir o caráter dinâmico da linguagem e popularizar essa área de investigação.--- DOI: http://dx.doi.org/10.22409/gragoata.2017n42a903

Spatiotemporal properties of magnetic fields induced by auditory speech sound imagery and perception.

Brain computer interface (BCI) technologies, which enable direct communication between the brain and external devices, have been developed. BCI technology can be utilized in neural prosthetics to restore impaired movement, including speech production. However, most of the BCI systems that have been developed are the "P300-speller" type, which can only detect objects that users direct his/her attention at. To develop more versatile BCI systems that can detect a user's intention or thoughts, the brain responses associated with verbal imagery need to be clarified. In this study, the brain magnetic fields associated with auditory verbal imagery and speech hearing were recorded using magnetoencephalography (MEG) carried out on 8 healthy adults. Although the magnetic fields lagged slightly and were long-lasting, significant deflections were observed even for verbal imagery, in the temporal regions, as well as for actual speech hearing. Also, sources for the deflections were localized in the association auditory cortices. Cross-correlations were calculated between envelopes of the imagined/presented speech sound and the evoked brain responses in the temporal areas. Measurable correlations were obtained for the presented speech sound; however, no significant correlations were observed for the imagined speech sound. These results indicate that auditory verbal imagery undoubtedly activates the auditory cortex, at least, and generates some observable neural responses.

Prosodic exaggeration within infant-directed speech: Consequences for vowel learnability.

Perceptual experiments with infants show that they adapt their perception of speech sounds toward the categories of the native language. How do infants learn these categories? For the most part, acoustic analyses of natural infant-directed speech have suggested that phonetic categories are not presented to learners as separable clusters of sounds in acoustic space. As a step toward explaining how infants begin to solve this problem, the current study proposes that the exaggerated prosody characteristic of infant-directed speech may highlight for infants certain speech-sound tokens that collectively form more readily identifiable categories. A database is presented, containing vowel measurements in a large sample of natural American English infant-directed speech. Analyses of the vowel space show that prosodic exaggeration in infant-directed speech has the potential to support distributional vowel learning by providing the learner with a subset of "high-quality" tokens that infants might attend to preferentially. Categorization models trained on prosodically exaggerated tokens outperformed models that were trained on tokens that were not exaggerated. Though focusing on more prominent, exaggerated tokens does not provide a solution to the categorization problem, it would make it easier to solve.

Effects of linguistic experience on brainstem encoding of speech sounds

Linguistic experience has been demonstrated repeatedly over the past decades as an important factor influencing the perception of speech sounds. At the behavioral level, speakers of different languages identify and discriminate speech sounds differentially (e.g., categorical perception). This has been observed at the cortical level as a reduced Mismatch Response, a measure that can reflect the sensitivity of the cortex to the differences between sounds. Yet, the effect of linguistic experience at an earlier stage of speech processing, namely, the brainstem, is scarcely studied. In the current study, we therefore aimed to examine specifically whether linguistic experience affects speech sound processing at the brainstem level. Twenty native Spanish speakers and twenty monolingual English speakers are recruited and their brainstem response to speech sounds will be measured with EEG. Specifically, we will use synthesized speech sounds: /ba/ with a + 10 ms and a -40 ms voice-onset-time (VOT). We hypothesize that while the encoding by the two groups will be similar for the + 10 ms /ba/ (common to English and Spanish), English speakers’ encoding of -40 ms prevoiced /ba/s (Spanish only) will be reduced relative to Spanish speakers. Data will be analyzed and interpreted with regards to these hypotheses.

Attentional modulation and domain-specificity underlying the neural organization of auditory categorical perception.

Categorical perception (CP) is highly evident in audition when listeners' perception of speech sounds abruptly shifts identity despite equidistant changes in stimulus acoustics. While CP is an inherent property of speech perception, how (if) it is expressed in other auditory modalities (e.g., music) is less clear. Moreover, prior neuroimaging studies have been equivocal on whether attentional engagement is necessary for the brain to categorically organize sound. To address these questions, we recorded neuroelectric brain responses [event-related potentials (ERPs)] from listeners as they rapidly categorized sounds along a speech and music continuum (active task) or during passive listening. Behaviorally, listeners' achieved sharper psychometric functions and faster identification for speech than musical stimuli, which was perceived in a continuous mode. Behavioral results coincided with stronger ERP differentiation between prototypical and ambiguous tokens (i.e., categorical processing) for speech but not for music. Neural correlates of CP were only observed when listeners actively attended to the auditory signal. These findings were corroborated by brain-behavior associations; changes in neural activity predicted more successful CP (psychometric slopes) for active but not passively evoked ERPs. Our results demonstrate auditory categorization is influenced by attention (active>passive) and is stronger for more familiar/overlearned stimulus domains (speech>music). In contrast to previous studies examining highly trained listeners (i.e., musicians), we infer that (i) CP skills are largely domain-specific and do not generalize to stimuli for which a listener has no immediate experience and (ii) categorical neural processing requires active engagement with the auditory stimulus.

Hacia un modelo multidimensional del trastorno específico del lenguaje y la dislexia: Déficits compartidos y específicos

Este artículo revisa la naturaleza y relaciones entre procesos implicados en el trastorno específico del lenguaje (TEL) y de la lectura (dislexia) en base a los criterios de clasificación del DSM-V. El TEL implica dificultades en la percepción y discriminación de los sonidos del habla, en la adquisición de vocabulario, así como en la comprensión y producción del lenguaje y de reglas gramaticales. La dislexia se incluye dentro de los trastornos de aprendizaje, y se caracteriza por una dificultad en la adquisición de las asociaciones entre letras y sus sonidos correspondientes y la fluidez o automatización lectora. Ambos trastornos se clasifican en categorías independientes y su posible interdependencia no queda clara. Recientes investigaciones han demostrado la presencia en ambos trastornos de un déficit de naturaleza fonológica que puede definirse en torno a dos dimensiones distintas aunque interrelacionadas: la habilidad para crear representaciones fonológicas y la habilidad para procesarlas y acceder a ellas. También se ha observado que ambos trastornos comparten dificultades atencionales, en la memoria de trabajo y en la velocidad de procesamiento, lo que explicaría la alta tasa de comorbilidad entre trastornos de lenguaje, lectura y atención. Estos hallazgos subrayan la naturaleza multidimensional de los trastornos y su ubicación en un continuum, suponiendo un reto para la perspectiva categórica de los actuales métodos de clasificación. Las nuevas investigaciones se orientan hacia el descubrimiento de características comunes y específicas de los trastornos. Éstas permitirán definir marcadores de riesgo tempranos, con claras implicaciones para la evaluación y tratamiento.

Vowels and Consonants in the Brain: Evidence from Magnetoencephalographic Studies on the N1m in Normal-Hearing Listeners

Speech sound perception is one of the most fascinating tasks performed by the human brain. It involves a mapping from continuous acoustic waveforms onto the discrete phonological units computed to store words in the mental lexicon. In this article, we review the magnetoencephalographic studies that have explored the timing and morphology of the N1m component to investigate how vowels and consonants are computed and represented within the auditory cortex. The neurons that are involved in the N1m act to construct a sensory memory of the stimulus due to spatially and temporally distributed activation patterns within the auditory cortex. Indeed, localization of auditory fields maps in animals and humans suggested two levels of sound coding, a tonotopy dimension for spectral properties and a tonochrony dimension for temporal properties of sounds. When the stimulus is a complex speech sound, tonotopy and tonochrony data may give important information to assess whether the speech sound parsing and decoding are generated by pure bottom-up reflection of acoustic differences or whether they are additionally affected by top-down processes related to phonological categories. Hints supporting pure bottom-up processing coexist with hints supporting top-down abstract phoneme representation. Actually, N1m data (amplitude, latency, source generators, and hemispheric distribution) are limited and do not help to disentangle the issue. The nature of these limitations is discussed. Moreover, neurophysiological studies on animals and neuroimaging studies on humans have been taken into consideration. We compare also the N1m findings with the investigation of the magnetic mismatch negativity (MMNm) component and with the analogous electrical components, the N1 and the MMN. We conclude that N1 seems more sensitive to capture lateralization and hierarchical processes than N1m, although the data are very preliminary. Finally, we suggest that MEG data should be integrated with EEG data in the light of the neural oscillations framework and we propose some concerns that should be addressed by future investigations if we want to closely line up language research with issues at the core of the functional brain mechanisms.

A dynamical framework to relate perceptual variability with multisensory information processing.

Multisensory processing involves participation of individual sensory streams, e.g., vision, audition to facilitate perception of environmental stimuli. An experimental realization of the underlying complexity is captured by the “McGurk-effect”- incongruent auditory and visual vocalization stimuli eliciting perception of illusory speech sounds. Further studies have established that time-delay between onset of auditory and visual signals (AV lag) and perturbations in the unisensory streams are key variables that modulate perception. However, as of now only few quantitative theoretical frameworks have been proposed to understand the interplay among these psychophysical variables or the neural systems level interactions that govern perceptual variability. Here, we propose a dynamic systems model consisting of the basic ingredients of any multisensory processing, two unisensory and one multisensory sub-system (nodes) as reported by several researchers. The nodes are connected such that biophysically inspired coupling parameters and time delays become key parameters of this network. We observed that zero AV lag results in maximum synchronization of constituent nodes and the degree of synchronization decreases when we have non-zero lags. The attractor states of this network can thus be interpreted as the facilitator for stabilizing specific perceptual experience. Thereby, the dynamic model presents a quantitative framework for understanding multisensory information processing.

Perception of height and categorization of Brazilian Portuguese front vowels

ABSTRACT Cross-linguistic typological observations and theoretical models in phonology suggest that certain speech sound distinctions are more complex then others. One such example is the opposition between mid-high and mid-low vowels, usually thought to be more complex than the opposition between high and mid vowels. The present study provides experimental evidence on speech sound perception which supports this notion. Native Brazilian Portuguese speakers performed vowel classification tasks involving either the distinction between the front high mid /e/ and the front high /i/, or the distinction between the front high mid /e/ and the front low mid /ε/ vowel. Measures of response time and discriminability (d') at the vowel category boundaries were obtained. Participants showed significantly slower responses and lower d' values in the "e-ε" as compared to the "i-e" classification task. Results indicate that perceptually distinguishing /e/ from /ı/ requires more processing time and resources, and involves more complex information than distinguishing /e/ from /i/.

Exploring the anatomical encoding of voice with a mathematical model of the vocal system

The faculty of language depends on the interplay between the production and perception of speech sounds. A relevant open question is whether the dimensions that organize voice perception in the brain are acoustical or depend on properties of the vocal system that produced it. One of the main empirical difficulties in answering this question is to generate sounds that vary along a continuum according to the anatomical properties the vocal apparatus that produced them. Here we use a mathematical model that offers the unique possibility of synthesizing vocal sounds by controlling a small set of anatomically based parameters.In a first stage the quality of the synthetic voice was evaluated. Using specific time traces for sub-glottal pressure and tension of the vocal folds, the synthetic voices generated perceptual responses, which are indistinguishable from those of real speech.The synthesizer was then used to investigate how the auditory cortex responds to the perception of voice depending on the anatomy of the vocal apparatus. Our fMRI results show that sounds are perceived as human vocalizations when produced by a vocal system that follows a simple relationship between the size of the vocal folds and the vocal tract. We found that these anatomical parameters encode the perceptual vocal identity (male, female, child) and show that the brain areas that respond to human speech also encode vocal identity.On the basis of these results, we propose that this low-dimensional model of the vocal system is capable of generating realistic voices and represents a novel tool to explore the voice perception with a precise control of the anatomical variables that generate speech. Furthermore, the model provides an explanation of how auditory cortices encode voices in terms of the anatomical parameters of the vocal system.

Involvement of superior temporal areas in audiovisual and audiomotor speech integration

Perception of speech sounds is affected by observing facial motion. Incongruence between speech sounds and watching somebody articulating may influence the perception of auditory syllable, referred to as the McGurk effect. We tested the degree to which silent articulation of a syllable also affects speech perception and searched for its neural correlates. Listeners were instructed to identify the auditory syllables /pa/ and /ta/ while silently articulating congruent/incongruent syllables or observing videos of a speaker’s face articulating them. As a baseline, we included an auditory-only condition without competing visual or sensorimotor input. As expected, perception of sounds degraded when incongruent syllables were observed, and also when they were silently articulated, albeit to a lesser extent. This degrading was accompanied by significant amplitude modulations in the beta frequency band in right superior temporal areas. In these areas, the event-related beta activity during congruent conditions was phase-locked to responses evoked during the auditory-only condition. We conclude that proper temporal alignment of different input streams in right superior temporal areas is mandatory for both audiovisual and audiomotor speech integration.

Effects of Corrective Feedback on Early and Late L2 Learners’ Perception of /θ/-/s/

This study explores whether both early and late second language (L2) learners are able to benefit from instructionthat includes corrective feedback (CF) on the perception of L2 speech sounds. It is a classroom-based study. Fourgroups of participants with less than 60% accuracy in the perception of /θ/-/s/ were recruited. They were allMandarin speakers of English. Group 1 (n=30, mean age: 21.23) and group 2 (n=16; mean age=20.31) began L2English study at or before 7 years old, whilst group 3 (n=29; mean age=19.48) and group 4 (n=17; mean age=20.56)started L2 English learning at or after the age of 12. Group 1 and group 3 went through a four-week programme ofform-focused lessons that drew their attention to the non-native contrast /θ/-/s/; they were given feedback during theawareness task. Group 2 and group 4 went through another four weeks of form-focused lessons with the sameinstruction and awareness tasks, except that no feedback was given during the awareness tasks. All the participants’accuracy regarding the perception of /θ/-/s/ was tested before the lessons (pre-test), immediately after the lessons(post-test), and one month after the lessons (delayed test). The results show that (1) compared with the pre-test, thefour groups all received some degree of improvement in the post-test and delayed test, yet group 1 and group 3displayed significantly higher accuracy than group 2 and group 4; (2) unexpectedly, the difference between group 1and group 3 as well as the difference between group 2 and group 4 was statistically insignificant. The findingssuggested that instruction with corrective feedback could be effective both in facilitating early and late learners’perception of non-native speech sounds. The effect of onset age on L2 learning, however, may not be overstated inL2 speech learning.